This invention relates to wiper control arrangements, in particular for motor vehicles, in which the position of wiper is detected and controlled.
German Offenlegungsschrift No. 32 08 121 discloses a wiper control arrangement having an electric motor with a reversible direction of rotation with a driven shaft to which at least one wiper arm is rigidly connected. The motor has a motor control circuit and a position regulator that produces a variable regulating signal for a motor switching circuit in which, on the one hand, the rotational position of the driven shaft of the motor is the controlled variable and, on the other hand, a specifiable path of the wiper motion is supplied as a time-dependent command variable to the position regulator. For determination of the controlled variable, a shaft-position indicator, rigidly coupled to the driven shaft of the motor, produces a signal representing the actual position of the driven shaft as an electrical variable, the shaft-position indicator constituting, for example, a potentiometer. A function generator supplying an output signal to the set value input of the position regulator generates the command variable. A periodic output signal having a voltage curve which is a function of time is produced at the output of the function generator. To produce variable wiping speeds, the function generator is controlled by an adjustable clock frequency which is obtained from a voltage-controlled oscillator. To vary the wiping angle, the voltage produced by the rotating generator must vary correspondingly. This is effected by an increase or decrease of the level of a direct voltage source supplied to the potentiometer so that the corresponding instantaneous value for the function generator is reached earlier or later, which results in reduction or increase of the wiping angle.
In wiper control arrangements, the problem arises that considerable wind forces act on the wiper arm or arms when, for example, a motor vehicle travels at high speed. As a result, the wiper arm, because of the applied wind forces, may move beyond its normal reversal point and only be able to reverse direction at a location beyond that point. As a result, the wiper blade fastened to the wiper arm may strike the window posts of the vehicle and cause corresponding damage. An additional risk is that the wiper arm may swing beyond the window posts and then operate abnormally.
To solve this problem, U.S. Pat. No. 5,287,585 discloses a wiper control arrangement that includes the following components: a rotatably supported main shaft to which a wiper arm is connected, a cam element fastened to the main shaft, a plate rotatably supported on a main lever by a first pin, a lower lever having one end that is arranged about the cam element and another end that is connected to the plate by a second pin, an arm rotatably supported on the plate by a third pin, the arm having an articulated section connected to a drive mechanism for the wiper, and a torsion spring acting between the plate and the arm to hold the arm in a specified position. In operation, the cam element rotates on an upper reversal point, urging the plate to turn, together with the arm, about the first pin by action of the lower lever. However, since the plate and the arm are connected with the wiper drive mechanism by the articulated section, the main lever turns. In other words, the position of the wiper arm at the upper reversal point is pushed back, with respect to the normal position, by a distance that corresponds to the angle of rotation of the main lever. Therefore, even when the wiper arm is moved by wind forces when the vehicle is moving at high speed, the motion of the wiper arm because of these wind forces is offset by the described arrangement so that the wiper arm reverses at its normal upper reversal point. Thus, the wiper arm can be prevented from striking the window posts without affecting the driver""s field of vision. The disadvantage of this wiper arrangement is its extremely complex mechanical design which leads to manufacturing difficulties and susceptibility to failure.
U.S. Pat. No. 4,934,014 discloses a wiper arrangement in which the wiping angle of the blade is reduced at high vehicle speeds to solve the problem. In this case, the wiper arrangement has a fixed structural part that is fastened to the vehicle body, a rotatably supported shaft, an arm connected to one end of the shaft carrying a wiper blade, a pivoting element connected to the other end of the shaft, a drive mechanism providing an angular oscillating motion of the pivoting element, an adjusting device for adjusting the connecting point between the pivoting element and the drive mechanism, and a control unit for driving the adjusting device as a function of vehicle speed and the angular speed of the pivoting element. The drive mechanism includes a first pin that is driven by a first motor around a circular path and which is functionally connected to a second pin which is moved by a bar connected to the pivoting element. Since the bar is displaced in a reciprocating motion by operation of the motor, the pivoting element is displaced by a pivoting motion about the axis of rotation of the shaft, which is rigidly connected to the pivoting element. The shaft is rotatably supported in the fixed structural part and an additional pin is moved by the pivoting element while an additional bar extends between that pin and a ball joint that is part of the adjusting device. The pivoting motion of the pivoting element displaces the bar in a reciprocating motion so that the pivoting element fastened to the shaft is also pivoted.
The adjusting device includes an additional motor with an additional rotatable shaft which is mounted on the pivoting element that is connected with the shaft drive mechanism and a worm wheel that is fixedly connected to the shaft of the adjusting device. The worm wheel meshes with another worm wheel fixedly mounted at one end of an additional shaft and an additional worm wheel that meshes with a toothed wheel is mounted at the other end of the additional shaft. The toothed wheel, the ball joint and a sensor with first and second sections are rotatably mounted on an additional common pin that is firmly connected to the pivoting element of the drive mechanism. The ball joint has an eccentric attachment by which the ball joint, upon rotation of the toothed wheel, can be turned on the pin together with the toothed wheel and the first section of the sensor.
Rotation of the ball joint by the pin causes the position of the connection point at which the bar is connected to the pivoting element to be varied. This variation results in a variation of the spacing between the connection point and the shaft. The variation of the angle of pivot of the pivoting element corresponding to this variation in spacing controls the angle of motion of the wiper blades which are rigidly connected to the pivoting element. This wiper control arrangement is disadvantageous because of its complex mechanical design, as well as the large number of components required including two motors.
Accordingly, it is an object of the invention to provide a wiper control arrangement which overcomes disadvantages of the prior art.
Another object of the invention is to provide a wiper control arrangement which is simple in design and in which striking of a wiper arm on a window post because of the wind forces generated by the speed of travel is prevented.
These and other objects of the invention arc attained by providing a wiper control arrangement in which operation of a wiper is controlled in response to a vehicle speed or wiper speed or position sensor. By providing a speed sensor for sensing vehicle wiper speed and generating a control signal which controls a wiper position regulator and/or the wiper operation angle and/or providing a detector for determining the position of the wiper device shaft in such a way that the adjusted wiping angle of the wiper is reduced at high vehicle speeds and/or high angular wiping speeds, no mechanical changes of any kind in the wiper control arrangement are necessary. Since the speed of a vehicle is determined in any event, the detected vehicle speed signal may be used so that essentially the only additional equipment requirement for application of the invention is wiring. Since the angular wiping speed is set by the wiper itself, that value is likewise known without requiring additional sensory analysis, so that equipment for detection of the angular wiping speed is already inherently present in the wiper arrangement.
In a preferred embodiment of the invention, the detector for determining the wiper position is a Hall generator, i.e., a device which produces a signal which varies as a function of the wiping angle based on the normal component of a magnetic field which varies with wiper position and which is detectable as Hall voltage variation as an input to a semiconductor chip. The advantage of such non-contacting position detection is that there is no wear of any kind, such as occurs in the sliding contacts of a potentiometer.